One major objective of the proposed investigation will be to document histological and ultrastructural changes occurring during normal secondary palate formation in man. Palatal shelves from human embryos and fetuses recovered from therapeutic abortions will be examined by light, scanning and transmission electron microscopy. The fine structure of the epithelial and mesenchymal components of the shelves will be determined at each stage prior to and during palatal closure. Another portion of the study will examine prefusion alterations in the epithelial surfaces involved in fusion in human and non-human species. The surface topography of palatal shelves prior to and during fusion will be examined by scanning electron microscopy. These observations will be correlated with observations based on examination of thin sections cut from the same specimens. The surface topography of shelves in vivo will be compared with shelves grown in vitro under varying conditions. Possible cellular migration on the shelf surface prior to contact and fusion in the human will also be examined by time- lapse cinematography of cultured shelves.